Yellow Phase of VT Secondary Earth

This sounds like it's stepped down for some unknown requirement, perhaps a control voltage or for powering monitoring equipment, or perhaps for making coffee, who knows....I don't see anything unusual, they just needed a neutral for the circuit, where else would you get one....This is going from 3Ø to a split phase supply and would supply 50v- 60v- 100v or 120 volts...

I'm sorry I put the question the wrong way and put too much detail.

I wanted to know why the 6.6kV/100V VT secondary Yellow phase is grounded for both metering and protection circuits and star neutral point is kept afloat.

Thanks

Yeah that's probably a code requirement, for safety....You wouldn't want a higher voltage source bleeding over to a lower voltage circuit in case of short...the neutral is probably grounded slightly upstream....

Maybe not enough detail. How many potential transformers do you have, and are you sure they are connected in star on the primary? Normal practice is to use 2 PTs connected in open delta, and Phase 2 is grounded for safety, to tie either Phase 1 & 3 at a fixed offset of 120V to Earth.

Supplying 3 potential transformers in each measurement location is unusual in U.S. practice, in switchgear. Normal is 2 connected open delta with phase 2 grounded. Supplying 3 transformers does make it easy to furnish polarizing voltage for ground fault detection on ungrounded systems, plus there is no phase shift with relays & meters, current vs voltage.

You should be able to ground any leg you want on the secondary of your PTs, just don’t ground the neutral also. I suspect the leg is grounded for personnel safety, and they chose to make it similar to the open delta de facto standard.

This is common practice in olden days with high resistance grounded or isolated systems.

Intention is the earth fault protection at generator terminals which is set sensitive should not maloperate for a phase-to-ground fault in VT secondary wiring.

IEEE 242 (Buff book) on protection & IEEE C37.101 & 102 on generator protection discuss this further.

If the earth faut protection is delayed, the y-phase grounding can be exempted.

Isn't grounding one phase of secondary of VT same as producing a phase-to-ground fault??

That's is true if the star point is also grounded.

...and not a <...fault...> in that case, because it is intentional.

Is this thread constrained to <...gentlemen...> for any particular reason or can others reply if they aren’t?

Haha